Without limiting the scope of the present invention, its background will be described with reference to downhole testing operations, as an example. It is well known in the subterranean well drilling and completion art to perform tests on formations intersected by a wellbore. Such tests are typically performed in order to determine geological or other physical properties of the formation and the fluid contained therein. For example, parameters such as permeability, porosity, fluid resistivity, temperature, pressure and saturation pressure may be determined. These and other characteristics of the formation and fluid contained therein may be determined by performing tests on the formation before the well is completed.
One type of testing procedure that is commonly performed is obtaining fluid samples from the formation to, among other things, determine the composition of the formation fluid. In this procedure, it is important to obtain samples of the formation fluid that are representative of the fluid, as it exists in the formation. In a typical sampling procedure, samples of the formation fluid may be obtained by lowering a sampling tool having one or more sampling chambers into the wellbore on a conveyance such as a wireline, slick line, coiled tubing, jointed tubing or the like. When the sampling tool reaches the desired depth, one or more ports are opened to allow collection of the formation fluid. The ports may be actuated in variety of ways such as by electrical, hydraulic or mechanical methods. Once the ports are opened, formation fluid enters the sampling tool such that samples of the formation fluid may be obtained within the sampling chambers. After the samples have been collected, the sampling tool may be withdrawn from the wellbore and the formation fluid samples may be analyzed.
It has been found, however, that as the fluid samples are retrieved to the surface, the temperature of the fluid samples may decrease causing shrinkage of the fluid samples and a reduction in the pressure of the fluid samples. These changes can cause the fluid samples to reach or drop below saturation pressure creating the possibility of asphaltene deposition and flashing of entrained gasses present in the fluid samples. Accordingly, once the sampling tool is retrieved to the surface and before the fluid samples are transferred to storage bottles, it is common to place the sampling chambers in a rocking stand, which tilts the sampling chambers up and down in a seesaw fashion to mix the fluid samples. To aid in mixing, heat may be applied to the sampling chambers. In addition, some sampling chambers include internal mixing balls that move through the fluid samples responsive to the force of gravity to aid in the mixing process.
It has been found, however, that mixing fluid samples using rocking stands can be a time consuming and difficult process. In order to achieve the desired mixing, sampling chambers often spend several days or weeks on the rocking stand. In addition, as the sampling chambers are in motion, it is difficult to obtain pressure readings associated with the fluid samples. Further, as the sampling chambers are typically quite long, the space required to perform a rocking operation for numerous sampling chambers is typically not available on the rig floor during offshore operations. Accordingly, a need has arisen for an improved method of mixing a fluid sample obtained in a downhole sampling chamber before the fluid sample is transferred to a storage bottle.